A new speaker project from Reinout

DSCN0526Currently i’m very happy running the Eimac 35TG amplifiers in combination with the open baffles (Feastrex and Fertin units). Serious bass, good soundstage and no aggressive highs. My primary source is as-we-speak under serious construction. At this stage i’m counting 340 kgs of turntable…..and it is not even running now….

But my issue is nowadays that i can not give a correct demonstration because i simply can AND will not bring the big loudspeakers to location X (with all the troubles of transport and possibilities of damage). Till now i used commercial speakers for demonstrating purposes but they were never really what i was looking for. They miss the natural presence of an open baffle (open baffle is not favoured by commercial loudspeaker brands) or miss dry-bass. Or are simply too expensive; remember that this set of speakers is only used a couple of times a year just for demonstrations. It is NOT the primary set loudspeakers.

My project this time:

* “portable” acceptable loudspeakers;
* Open baffle (sorry….i like this concept);
* 2-way system; the crossover is soo much more easy;
* High sensitivity; logical as i only use tube amps;

At Ebay i scored a nice set of Supravox 285GMF. Wonderfull classical build-up (paper cone, serious magnet, sturdy basket) and of much more importance a usable frequency range of 40 Hz to 7kHz. Especially the high crossover frequency is interesting as i really really did not want to be in the 1-3 kHz for crossover-purposes. In this area the human ear (mine anyways) is remarkable sensitive and i don’t like the fact that a unit will take over from another unit….you can hear it….so it is annoying !

Next thing was to score a mid/high unit and a proffesional FaitalPro compression driver was looking perfectly suitable. Amazing smooth frequency response from 4 kHz upwards. The real issue here was the dispersion of those highs. Horns have a tendency to have a coloured sound so i was looking for something different to be used. I’ve found a very very old Karslon K-coupler perfectly to do the job. Dr. Karlson is especially known for his bas-cabinets but the theory of his research is easily extended to higher frequencies. With a cast-aluminium K-coupler i’m able to project mid and high frequencies from 2 kHz upwards. And as the FaitalPro’s are nicely usable from 4 kHz upwards this seemed a nice match.

The crossover-frequency was already set a 4 kHz; for both to be used speaker-units to be used completely within acceptable parameters. The efficency of the units is way-off; i needed to bridge 14 dB ! normally a resistor-network will do this tricj but resistors means burning energy and in this high efficiency 2-way design i like to conserve energy. Silvercore autoformers were the logical choice to match/mate the 2 units in combination with an extremely simply 1st order crossover. A single coil for the bass/mid; a single capacitor (+ Silvercore autoformer) for the mid/highs….that’s all.

The crossover is build upon the leftovers from the woodwork.

The FaitalPro + K-coupler is fixed with a modular build-up to the open baffle “box”. That box itself is made from 40 mm and 25 mm plywood. The connection between the box and the FaitalPro is made from a headrest belonging to a wheelchair……


Very happy with the result:

* Dry bass;
* Good placement/location;
* Effortless music; no stress.

So for the next ETF i have my demo-speakers ready !

Regards, Reinouyt

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